Magnetostrictive actuators are devices in which materials that undergo magnetostriction are used to produce an output strain in response to a magnetic driving force. Magnetostriction is the name given to the process whereby some materials alter their physical dimensions when a magnetic field is applied to them. Thus these materials offer the opportunity to convert electrical energy into mechanical energy.
By doping iron with gallium, U.S. Navy researchers created Galfenol, a material that has enhanced magnetostrictive properties. The added gallium enhanced iron's magnetostrictive capability tenfold. The addition of gallium to the iron changes the structure of the iron, which on an atomic level forms a lattice of regular cubic cells. When the gallium combines with the iron, the faces of some of the cells become rectangular rather than square. These elongated gallium-iron cells then congregate into tiny clumps within the lattice. These clusters of distorted cells respond to a magnetic field by rotating their magnetic moments, like tiny compass needles.
The prior art does not teach a method or apparatus that optimizes Galfenol-type magnetostrictive actuators. The prior art U.S. Pat. No. 7,218,067 (the '067 patent) teaches an arrangement including orthogonal coils. However the coils are not arranged in a manner that optimizes the magnetic moments available in Galfenol-type magnetostrictive actuators. FIG. 6A is an explanatory illustration of the teaching of the '067 patent. As shown in FIG. 6A, the '067 patent arrangement includes first and second orthogonally positioned coils 410 and 420 surrounding a magnetic field-actuated material 450. As shown, the coils (410, 420) have a diameter d, and the material 450 has a length l. FIG. 6A also shows a dashed circle 401 illustrating the localized magnetic field, according to the '067 patent. Thus, '067 patent produces only a localized field, and does not affect the entire length of the magnetic field-actuated material 450. Thus in working conditions, only those portions of the material 450 within the vicinity of the localized magnetic field would be influenced by the field. Consequently, the FIG. 4A arrangement does not optimize the use of the entire length of the material 450.
FIG. 6B shows a possible arrangement based on the '067 patent, in which the entire material 450 is influenced by the magnetic field. As shown, this is achieved by having orthogonal coils 430 and 440 having an increased diameter D with respect to the material 450 having a length l, as stated above. According to the arrangement in FIG. 4B, the magnetic flux generated engulfs the magnetic field-actuated material 450. FIG. 4B also shows a dashed circle 403 representing the localized magnetic flux generated by the coils 430 and 440. As shown this area extends well outside the bounds of the material 450, which is extremely inefficient, resulting in a low strength magnetic field acting on the material 450. Consequently, it is desired to have an arrangement that optimizes the magnetic moments available in Galfenol-type magnetostrictive actuators, in an energy efficient manner.